What I mainly do is adding texture (via a multiply layer) and fiddle with light and contrast (levels, curves). I nearly always as well add the oil paint filter to the map. This makes the map look a bit more hand painted and not computer generated. It also helps free hand objects added to the map in PS melt into the style a bit. Lately I've also started adding all rivers in PS, gives you more control and I like that the rivers can differ in width a bit when the float down to the sea/ocean.
That is mainly what i do, it might differ a bit between maps.